Blind rivet having a bore defined by a plurality of flat walls



Nov. 27, 1962 R. F. KoLEc ETAL 3,065,661

I BLIND RIVET HAVING A BORE DEF' INED BY A PLURALITY oF FLAT WALLS.

3 Sheets-Sheet 1 Filed OCT.. 13. 1.959

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3/ Fie/Q 4r-runways ,f lae/s, .7d/sca, Rassen en/vf Nov. 27,l 1962 R. F. KoLEc ETAL 3,065,661 BLIND RIVET HAVING A BORE DEFINED BY Y A PLURALITY OF FLAT WALLS Filed Oct. 15. 1959 3 Sheets-Sheet 2 Marg. Maui.

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t 3,065,661 Patented Nov. 27, 1962 3,065,661 BLIND RIVET HAVING A EURE DEFINED BY A PLURALITY F FLAT WALLS Robert F. Kolec, Whittier, and Vernon L. Dunham, Anaheim, Calif., assignors to @lympic Screw & Rivet Corporation, Downey, Calif., a corporation of California Filed Get. 13, 1959, Ser. No. 846,102, 3 Claims. (Cl. 8540) The present invention relates in general to a blind rivet assembly and to a method of manufacturing a component of such an assembly, a primary object of the invention being to provide a blind rivet assembly capable of producing high' clinching forces when set. This application is a continuation-in-part of our copending application Serial No. 827,876, tiled July 17, 1959.

As general background, a blind rivet assembly of the type to which the invention relates comprises a pin having thereon a tubular rivet which includes a sleeve having a head at one end and a tail at its other end, the pin being provided at one end thereof with rivet expanding means adjacent and engageable with the tail of the tubular rivet and being provided with grippable means at the other ends thereof. Preferably, `the pin is provided with an enlarged shank terminating in a further enlarged head to form the rivet expanding means and is provided with a weakened zone or break neck intermediate such shank and the grippable means.

In setting a rivet assembly of the foregoing character, the assembly is inserted through registering holes in elements to be riveted together so that the tail of the tubular rivet and the head on the pin are on the blind or inaccessible side of such elements and the head of the tubular rivet and the grippable means on the pin are on the opposite side thereof. A riveting tool having pressure and pulling members is applied to the rivet assembly with the pressure member seated against the head of the tubular rivet and with the pulling member in engagement with the grippable means on the pin. The pulling member is then moved axially of the pressure member to draw the head on the pin into tail expanding or flaring engagement with the Itail of the tubular rivet, thereby clamping the elements which are to be riveted together between the head of the tubular rivet and the expanded or flared tail thereof. Eventually, the pin of the rivet assembly snaps at the break neck therein, upon completion ofthe setting of the rivet assembly, and any excess portion of the pin may be trimmed olf flush with the head of the tubular rivet.

An important object of the present invention is to provide a rivet assembly of the foregoing nature wherein the tubular rivet is internally weakened along circumferentially spaced, longitudinal lines from the tail of the rivet toward the head thereof so that, as the head on the pin is drawn into the sleeve, it splits the sleeve longitudinally along the internal longitudinal lines of weakness into a plurality of prongs which engage the blind side of the assembly of elements to be riveted together. As the head on the pin splits the sleeve into prongs, it also spreads the prongs in such a manner that the prongs clamp the elements to be riveted together firmly against the head of the tubular rivet with a wedging action, which is an important feature.

Another object is to longitudinally weaken the sleeve of the tubular rivet internally from the tail toward the head by providing the rivet with an internal cross section in this region which is noncircular and which has apices forming the internal longitudinal lines of wea-kness mentioned. More particularly, an object in this connection is to provide the tubular rivet with an axial hole extending from the tail toward the head Which is polygonal in cross section, the apices of the resulting polygon forming the internal longitudinal lines of weakness along which lthe sleeve splits. While the polygonal hole in the tail end of the tubular rivet may have as few as three sides, or more than four sides, such hole is preferably a four-sided, substantially square one.

Another important object of the invention is to provide a method of forming a tubular rivet of the foregoing nature from a solid cylindrical bar of material which comprises punching the aforementioned polygonal hole in one end of the bar to a depth approaching the distance between the tail and the head of the finished tubular rivet, the opposite end of the bar being upset to form the head and the polygonal hole being extended the rest of the way through the bar, as a circular hole, to render the nished rivet tubular. Preferably, the circular internal portion of the ltubular rivet is also formed by punching.

As the result of the aforementioned punching operations, and particularly the one utilized to form the polygonal hole in the tail end of the rivet, the material of the sleeve at the internal surface thereof is placed in a state of axial compression relative to the material of the sleeve at the external surface thereof. Consequently, when the sleeve is split into prongs by the head on the pin in setting the rivet assembly, the stress differential between the internal and external surfaces of the prongs causes them to curl outwardly through substantially so that the ends of the prongs seat against the blind side of the assembly of elements being riveted together. This outward curling of the prongs, due to the built-in axial stress differential between the internal and external surfaces of the sleeve during manufacture, assists the hereinbefore mentioned wedging action of the prongs in producing extremely high clinching forces and represents an important feature of the invention. v

Another object of the invention is to provide thehead on the pin with a divergent annular surface of concave cross section which engages the internal surface of the sleeve to force the prongs outwardly upon splitting of the sleeve and which is so shaped as to assist the aforementioned axial stress diferential in curling the prongs outwardly and axially toward the head of the tubular rivet, and which is also so shaped as to spread the prongs to wedge the elements to be riveted together -iir-mly against the head ofthe tubular rivet.

An object in connection with one embodiment of the invention is to provide the tail of the tubular rivet with radial grooves or notches which extend from the internal surface of the sleeve to the external surface thereof and at least some of which are respectively adjacent the apices of the square or other polygonal hole in the tail end of the tubular rivet. Preferably, the number of such radial grooves considerably exceeds the numbers of apices of the polygonal hole so that some of the grooves will always be adjacent the respective apices of the polygonal hole to facilitate initiation of splitting of the sleeve into prongs. With this construction, it is not necessary to position'the radial grooves in the tail accurately relative to the apices of the polygonal hole in the circumferential direction, enough such radial grooves being provided that there will always' be one closely adjacent each apex.

An object in connection with another embodiment of the invention is to bevel or chamfer the `tail of the tubular rivet externally to provide it with a thin annular edge adjacent the periphery of the square or other polygonal hole in the tail and of the tubular rivet. This thin annular 0 edge is weakened by the apices of the polygonal hole so that splitting of the tail end of the tubular rivet into prongs lhead on the pin into the tail end of the rivet slightly during assembly to start the desired splitting, i.e., to presplit the tail end of the rivet.

More generally, an important object of the invention is to pre-split the tail end of the rivet slightly at the ends of the internal longitudinal apices therein to facilitate spliting of the rivet by the head on the pin during setting of the rivet assembly, such pre-splitting of the tail end of 4the rivet being accomplished either by the head on the pin during assembly of the rivet and the pin, or being accomplished prior to assembly of the rivet and the pin by suitable tools designed for the purpose.

As previously mentioned, the internal surface of the hole through the tubular rivet is polygonal only from the tail of the rivet substantially to the head thereof, the internal surface of the rivet being circular within and adjacent `the head. Providing the tubular rivet with a circular hole in this region results in maximum resistance to hoop stresses to prevent failure upon drawing the shank of the pin into the head end of the rivet, which is an important feature. Another object in this connection is to provide the shank of the pin with retaining means, such as annular or longitudinal ribs, engageable with the walls of the polygonal hole prior to setting of the rivet assembly to hold the pin and the tubular rivet in assembled relation, and engageable with the wall of the circular hole in the head end of the rivet to assist in locking the pin in place in the tubular rivet after the rivet assembly is set, wherefore no swaging of the head onto the pin is needed.

The foregoing objects, advantages, features and results of the present invention, together with various other objects, advantages, features and results which will be evident to those skilled in the blind rivet art in the light of this disclosure, may be achieved with the exemplary embodiments of the invention described in detail hereinafter and illustrated in the accompanying drawings, in which: y

FIG. l is a view, partially in elevation and partially in longitudinal section, illustrating a solid cylindrical blank, from which the tubular rivet of the invention is to be formed, cut from a length of bar stock;

FIG. 2 is a longitudinal sectional view illustrating the li'rst step in forming the tubular rivet from the blank;

FIG. 3 is a longitudinal sectional view illustrating the second step in forming the tubular rivet, FIG. 3 being Vtaken along the arrowed line 3-3 of FIG. 4;

FIG. 4 is a transverse sectional view taken along the arrowed line 4-4 of FIG. 3;

FIG. 5 is an elevational view of a punch for punching an axial polygonal hole in one end of the blank to produce the structure of FIG. 3;

FIG. 6 is a longitudinal sectional view illustrating the third step in the formation of the tubular rivet from the blank;

FIG. 7 is a longitudinal sectional view illustrating the fourth and final step in forming the tubular rivet;

`FIG. 8 is an end elevational view taken as indicated by the arrowed line 8--8 of FIG. 7;

FIG. 9 is a longitudinal sectional view illustrating the first step in the setting of a blind rivet assembly of the invention, which blind rivet assembly includes the tubular rivet above referred to;

FIG. 10 is a transverse sectional view taken along the arrowed line 10-10 of FIG. 9;

FIG. 11 is a longitudinal sectional view illustrating the blind rivet assembly in partially set condition;

FIG. l2 is a longitudinalsectional view illustrating the blind rivet assembly in fully set condition;

FIG. 13 is a longitudinal sectional view illustrating the set blind rivet assembly after trimming olf excess material from a pin of the assembly;

FIG. 14 is an end elevational view of the set blind rivet assembly, FIG. 14 being of the bottom end of the rivet assembly as it is viewed in FIG. 13;

FIG. 15 is an elevational view of an alternative pin for the blind rivet assembly of the invention;

FIG. 16 is a longitudinal sectional view similar to FIG. 7, but showing another tubular rivet embodiment of the invention;

FIG. 17 is a longitudinal sectional view similar to FIG. 7, but showing still another tubular rivet embodiment of the invention;

FIG. 18 is a longitudinal sectional view similar to FIG. 9, but showing a rivet assembly incorporating the tubular rivet of FIG. 17;

FIG. 19 is a longitudinal sectional view taken along the arrowed line 19-19 of FIG. 18;

FIG. 20 is a longitudinal sectional View similar to FIG. 17 and showing another tubular rivet embodiment of the invention;

FIG. 2l is a longitudinal sectional view showing presplitting of the tail of the tubular rivet of FIG. 20;

FIG. 22 is an enlarged, end view of the tail of the tubular rivet of FIGS. 20 and 2l after pre-splitting thereof;

FIG. 23 is a fragmentary longitudinal sectional view taken along the arrowed line 23-23 of FIG. 22;

FIG. 24 is a longitudinal sectional view similar to FIG. 20;

FIG. 25 is a longitudinal sectional view similar to FIG. 21, but showing another means for pre-splitting the tail of the tubular rivet shown in FIG. 24;

FIG. 26 is an enlarged end view of a tool used in the pre-splitting operation shown in FIG. 25;

FIG. 27 is an enlarged, fragmentary internal elevational view of the pre-split tubular rivet of FIG. 25 showing a split therein;

FIG. 2S is a longitudinal sectional view similar to FIG. 20, but showing still another tubular rivet embodiment of the invention;

FIG. 29 is a longitudinal sectional view similar to FIG. 25, but showing pre-splitting of the tail of the tubular rivet of FIG. 28;

FIG. 30 is a longitudinal sectional view showing yet another tubular rivet embodiment of the invention; and

FIG. 31 is a transverse sectional View taken along the arrowed line 31--31 of FIG. 30.

Referring first to FIG. 9 of the drawings, the completed blind rivet assembly of the invention is designated generally by the numeral 2@ and includes a pin 22 having thereon a tubular rivet 24. The latter includes a sleeve 26 having a tail 28 and a head 30 at opposite ends thereof, the head being shown as including a central boss 31 and an annular flange 32. However, the head 30 may have the vconfiguration of the head 30a of the tubular rivet 24a of FIG. 16, the rivet 24a being otherwise identical to the rivet 24, or the head 30 may have some other configuration. A

lsealing washer 33 is shown as carried by the sleeve 26 in engagement with the head 30, or, more particularly, in engagement with an annular shoulder 34 formed by the head and facing in the direction of the tail 28, for installations in which a fluid-tight seal is required.

The sleeve 26 is provided with an axial polygonal hole 36, preferably a substantially square hole, which extends from the tail 28 substantially to, but preferably terminates short of, the head 30. The apices or corners 38 of the square hole 36 provide the interior of the sleeve 26 with circumferentially spaced, longitudinal lines of weakness extending from the tail 28 toward, but preferably termimating short of, the head 30. As will be discussed in detail hereinafter, the corners 38 of the square hole 36 provide longitudinal lines of weakness along which the sleeve 26 is adapted to split from the tail 28 toward the head 30.

The square hole 36 terminates at its inner end in a hole 40 of circular cross section which extends the rest of the way through the tubular rivet 24 and is located within the head 30. Making the hole 40 circular in cross section provides maximum strength with reference to hoop stresses in this region, the tubular rivet 24 being subjected to such E stresses in setting of the blind rivet assembly 20 as discussed hereinafter.

The pin 22 is provided at one end thereof with means for expanding the tubular rivet 24 into engagement with the assembly of elements to be riveted together and for expanding the tail 28 of the tubular rivet into clinching engagement with the blind side of such assembly of elements. This expanding means includes an enlarged shank 42 which terminates in a further enlarged head 44, the latter having divergent annular surfaces 45 and 46 for tail flaring engagement with the tail 2S of the sleeve 26. The annular surface 45 is relatively acute and the annular surface 46 is relatively obtuse so that these surfaces, together, approach an arcuate, concave surface in cross section. The shank 42 tapers into the body of the pin 22, as indicated at 47, and the shank is annularly ribbed, as indicated at 48, to provide a gripping means engageable with the wall of the circular hole 40v in the tubular rivet 24 when the blind rivet assembly Ztl is set, thereby preventing dislodgement of the pin. The annularly ribbed portion 48 of the shank 42 also engages the sides of the square hole 36 prior to setting, as most accurately shown in PEG. l0, to hold the pin 22 and the rivet 24 together during shipment, handling, and the like. FIG. l shows a pin 22a having a longitudinally ribbed portion 48a which achieves similar results.

Adjacent the shank 42 of the pin 22 is a weakened zone or break neck 49, preferably in the form of an annular groove, the pin 22 being adapted to snap at this point when the blind rivet assembly 2d is set. The pin 22 is provided, at the end thereof opposite the head 44, with grippable means 50, the means Sti being engageable by a gripping means on the pulling member of a riveting tool to be described. In the particular construction illustrated, the grippable means 5t) comprises a plurality of annular ribs on the pin 22 formed by annularly grooving the pin.

The foregoing completes an over-all description of the rivet assembly 2&9 and the manner in which the tubular rivet 24 is formed will now be considered.

Referring to FIG. l of the drawings, the starting material is preferably cylindrical bar stock 5l, which may be of any suitable material, such as aluminum, or an aluminum alloy. From the bar stock 5l is cut a blank 52 of appropriate length, the length of the blank depending on the length desired for the tubular rivet 24 and the length of the latter being determined by the thickness of the assembly of elements with which it is to be used.

Referring now to FlG. 2 of the drawings, the blank 52 is placed in suitable dies, not shown, which punch an axial hole S4 in one end of the blank, this hole being of circular cross section. Preferably, a central axial indentation 56 is simultaneously punched in the opposite end of the blank S2 by such dies. By comparing FIGS. l and 2, it will be noted that the blank 52 has been lengthened slightly as the result of displacement of the material of the blank in forming the hole 54.

Turning to FIGS. 3, 4 and 5 of the drawings, the blank 52 is next placed in dies, not completely shown, which include -a punch 58 for punching the square, or other polygonal, hole 36 in the blank, the square hole 36 being punched in the same end of the blank as the indentation 56. It will be noted that the displacement of material resulting from punching of the square hole 36` produces considerably elongation of the blank 52 by extrusion of the material of the blank along the punch 58. The depth of the square hole 36 is such as to extend this hole from the tail 2S of the finished tubular rivet 24 substantially to, but preferably terminating short of, the head 30. For the particular head configuration shown in the drawings, the square hole 36 extends about half the length of the blank -52 in the FIG. 3 condition of the blank.

To facilitate metal flow around the punch 58 and to facilitate withdrawal of the punch from the square hole 36, the tip of the punch is provided with a slightly en larged head 59 and the sides of the punch are beveled slightly adjacent the corners of the punch, the beveled surfaces being designated by the numeral 60. The bevel angle may, for example, be of the order of 7.

Referring to FG. 6r of the drawings, the blank 52 is next placed in dies, not shown, which partially head the end of the blank opposite the square hole 36 therein. Such dies include a punch, not shown, which tits into the previously punched hole 54 in the head end of the blank 52, and include a punch, not shown, of circular cross section which ts into the square hole 36 and forms at the inner end thereof a hole 62 of circular cross section, the hole 62 constituting an extension of the square hole and preferably being of substantially the same diameter as the hole 54. It will be understood that the downward forces applied to produce the partially formed head of FIG. 6 are resisted by upward `forces applied to the punch which forms the circular hole 62. Thus, the desired square configuration for the hole 36 is preserved.

Finally, as shown in FIG. 7, the blank 52 is placed in dies which provide the 4finished head 30 and which punch out the material separating the holes S4 and 62 so as to provide through the head 30 of the rivet the hole 40 of circular cross section. However, the hole 40 may be at least partially a drilled hole. At the same time, the tail 28 of the resulting tubular rivet 24 is radially grooved or scored in a plurality of locations, the resulting radial grooves being designated by the numeral 66 and there being a sucient number of such grooves that each corner of the square hole 36 will have such a groove closely thereadjacent. This avoids any necessity for rotationally indexing the blank 52 and the die which forms the radial grooves 66, there being a sufficient number of the grooves in question that some of them are close enough to the respective corners 38 of the square hole 36 to initiate splitting of the sleeve 26 of the rivet 24 along the corners of the square hole.

It will be noted that at least the square hole 36, and preferably both the square hole and the circular hole 40, are formed entirely from axial punching operations. The effect of this is to compact the lmaterial of the tubular rivet 24 adjacent its inner surface relative to the material of the rivet adjacent its outer surface. In other words, the material of the tubular rivet 24 at the internal surfaces of the square and circular holes 36 and 4t), and particularly the surfaces of the square hole 36, is in `a state of axial compression relative to the material of the tubular rivet at the external surfaces thereof. The effect of this will be discussed hereinafter.

Considering now the setting of the rivet assembly 20, the pin 22 and the tubular rivet 24 formed by the foregoing operations are assembled in the manner shown in FIG. 9 of the drawings and described previously. The resulting blind rivet assembly 20 is inserted into registering holes 72 and 74 through elements 76 and 78 which are to be riveted together to form a riveted assembly 3%, FIGS. l2 and 13. When the rivet assembly 20' is thus inserted into the holes 72 and 74, the tail 28 of the tubular rivet 24 and the head 44 of the pin 22 are disposed on the blind side of the assembly 80, while the head 30 of the tubular rivet 24 and the grippable means 50 on the pin 22 are disposed on the accessible side of the assembly. The washer 33, if used, under the head 30 is engageable with the accessible side of the assembly $0.

With the rivet assembly 20 inserted through the work assembly in the foregoing manner, a suitable riveting tool 82 is lapplied to the rivet assembly. More particularly, the riveting tool 82 is provided with a pressure member or anvil 84 adapted to seat on the head 30 and is provided with a pulling member 86 which is movable axially of the pressure member and which is provided with gripping means 88 engageable with the grippable means S0 on the pin 22 of the rivet assembly. The foregoing conditions obtaining, the pulling member 86 is moved axially of the pressure member 84 in a direction away from the work assembly y8) to pull the pin 22 into the sleeve 26 of the tubular rivet 24.

Referring to FIGS. 11 and 12, as the pin 22 is moved axially of the tubular rivet 24 to pull the enlarged shank 42 into the head end of the sleeve 26 and the head 44 on the pin 22 into the tail end of the sleeve 2K6', the enlarged shank 42 expands the head end of the sleeve 26 and the head 44 on the pin 22 splits the sleeve 26 into prongs 90 along the corners 38 of the square hole 36, the splitting starting at the respective radial grooves 66 which are nearest the corners. The head 44 on the pin 22 also spreads or flares the prongs 90 to cause them to act on the blind side of the element 78 with a wedging action to clamp the elements 76 and 78 between the prongs and the head 30. At the same time, the sleeve is expanded to substantially fill the holes 72 and 74.

The prongs 90 curl outwardly and axially toward the work assembly 80 and into additional clamping or clinching engagement with the blind side thereof, as shown in FIGS. 12 and 13. Such curling of the prongs 90 is augmented by the effectively concave cross section of the pin 22 at the junction between the shank 42 and the head 44, but is due primarily to the axial stress differential between the internal and external surfaces of the square hole 36. As previously pointed out, the axial compaction of the blank 52 in forming the tubular rivet 24 results in placing the internal surfaces of the square hole 36 in particular in a state of axial compression relative to the external surface of the sleeve 26 in the vicinity of the square hole. Consequently, when the sleeve 26 is split into the prongs 90, the latter are subjected to this same axial stress differential, the internal surfaces o-f the prongs tending to elongate and the external surfaces thereof to contract to relieve the axial stress differential. Consequently, the prongs 90 curl into the positions shown in FIGS. 12 and 13 and, in so doing, supplement the wedging action described previously to clamp the work assembly very tightly between the prongs and the head 3) of the tubular rivet 24.

It will be noted that the annularly ribbed portion 48 of the shank 142 of the pin 22 is disposed in the circular hole 62 through the head end of the tubular rivet 24. This has the effect of retaining the pin in the position shown in FIGS. 12 and 13.

When the pin 22 expands the tubular rivet 24 to fill the holes 72 and 74, relatively high hoop stresses are developed in the expanded portion. Adequate resistance to such hoop stresses is provided by making the hole 40 in the head of the rivet 24 of circular cross section, instead of extending the square hole 36 entirely through the rivet. Thus, the square hole 36 is provided only throughout the length of the tubular rivet 24 which is to be split, at least the major portion of the remaining length of the tubular rivet being provided with the circular hole 4t) to prevent hoop stress failure of the unsplit portion of the tubular rivet 24.

As shown in FIG. 12, when the pin 22 arrives at its final position, the resistance to further axial movement thereof reaches a value such that the pin snaps at the break neck 49. As a final operation, the pin 22 may be trimmed off flush with the head 30 of the tubular rivet '24, as shown in FIG. 13 of the drawings.

Referring to FIGS. 17 to 19 of the drawings, illustrated therein is a rivet assembly 120 which is similar to the assembly 20, the components of the assembly 120 being identified by numerals higher by 100 than those used to identify the corresponding components of the assembly 20. Only those components of the assembly 120 differing from the corresponding components of the assembly will be described specifically.

The assembly 120 differs from the assembly 20 only in that the tail 128 of the tubular rivet 124 is externally bevelled or chamfered, as indicated at 152, instead of being provided with the radial grooves 66 of the tail 28. Externally bevelling the tail 128 provides it with a thin annular edge 154 adjacent the periphery of the square or other polygonal hole 136. Further, a slight burr 156 is formed which extends into the hole 136. When the rivet 124 and the pin 122 are assembled, as shown in FIGS. 18 and 19, the burr 156 is displaced outwardly, as best shown in FIG. 19, by the effectively concave junction of the shank 142 and the head 144 of the pin 122, to presplit the thin edge 154 at the apices of the hole 136, as indicated at 158 in FIG. 18. However, even without the burr 156, the thin edge 154 is normally pre-split at the apices of the hole 1'36 upon assembly `of the pin 122 and the rivet 124.

Referring to FIGS. 20 to 23 of the drawings, illustrated therein is a tubular rivet 160 comprising a sleeve 162 having a tail 164 and a head 166 at opposite ends thereof. The internal surface of the sleeve 162 is provided with circumferentially spaced longitudinal lines of weakness 168 extending from the tail 164 substantially to, but preferably terminating short of, the head 166. The lines of weakness 168 may be the apices or corners 168 of a polygonal hole 170 in the sleeve 162, such polygonal hole being extended through the head 166 as a round hole 172.

The tail 164 is externally beveled or chamfered, as shown at 174, and, prior to assembling the tubular rivet 160 with a pin, such as the pin 122, for setting it, the tail 164 is pre-split at the ends of the longitudinal corners 168, the splits being designated by the numeral 176 and being similar to the splits 158 of the tubular rivet 124 of FIGS. 17 to 19. However, instead of being formed by a pin, such as the pin 22, the splits 176 are formed by a suitable tool during manufacture, such as the tool 178 of FIG. 21. The tool 178, which may have various configurations other than the one shown, is provided with a convergent annular surface 180 which engages the internal surface of the sleeve 162 at the tail 164 to form the splits 176 in much the same manner that the pin 122 forms the splits 158 in the tubular rivet 124 of FIGS. 17 to 19.

Referring to FIGS. 24 to 27, illustrated therein is a tubular rivet which is substantially identical to the tubular rivet 160 so that the same reference numerals will be utilized to designate the various components thereof. The tail 164 of the tubular rivet 190 is pre-split at the ends of the longitudinal corners 168, the splits being designated by the numeral 192. In this case, the splits 192 are formed by a cutting tool 194 having a cruciform cutting edge 196 adapted to be aligned with the tail ends of the corners 168 and to be forced into the tail 164 to form the splits 192. The tool 194 is shown diagrammatically as having a flat cruciform cutting edge 196, it being understood that such cruciform cutting edge may be formed on a convergent tool so that the cruciform cutting edge tapers toward its center. In this instance, the tool will pre-split the tail 164 of the rivet 190 more deeply at the internal surface of the rivet than at the external surface thereof.

l FIGS. 28 and 29 show a tubular rivet 200 which is similar to the tubular rivet 160 so that identical numerals are utilized to designate corresponding components, the only difference between the rivet 200 and the rivet 160 being that the tail 164 of the rivet 200 is in a plane perpendicular to the axis of the rivet, instead of being externally beveled or chamfered. A tool 202 similar to the tool 194 is utilized to pre-split the tail 164 of the rivet 260 at the tail ends of the corners 168 thereof, such splits being designated by the numeral 204.

Referring to FIGS. 30 and 31 of the drawings, illustrated therein is a tubular rivet 210 of the invention which includes a sleeve 212 having a tail 214 and a head 216 at opposite ends thereof. In this embodiment, the rivet 210 is provided with an axial hole 218 of circular cross section extending entirely therethrough. The wall of the hole 218 is provided with circumferentially spaced, longitudinal apices 220 which extend from the 9 tail 214 toward the head 216, but which preferably terminate short of the head. In this case, the apices 220 are substantially V-shaped and are formed directly in a cylindrical internal surface of the sleeve 212, instead of be ing formed by the apices or corners of a polygonal hole in the sleeve. The tail 214 of the rivet 210 is shown as provided with a rounded external bevel or chamfer 222 and is shown as provided with splits 224 at the tail ends of the apices 220.

It will be understood that the various alternative tilbular rivet embodiments hereinbefore described are formed in substantially the same manner as and operate in substantially the same manner as the tubular rivet 24, further description therefore being unnecessary.

Although exemplary embodiments of the invention have been disclosed herein for purposes of illustration, it will be understood that various changes, modifications and substitutions may be incorporated in such embodiments without departing from the spirit of the invention as dened by the following claims.

We claim:

l. In a blind rivet assembly, the combination of:

(A) a tubular rivet capable of permanent deformation and including (a) an externally cylindrical sleeve provided with a through bore and having at one end thereof a head with a transverse annular shoulder which faces the other end of said sleeve,

(b) the bore of said sleeve, between said other end thereof and a transverse plane adjacent said head, being defined by at least three substantially flat walls of substantially equal widths extending from said other end of said sleeve to said transverse plane,

(c) said walls intersecting at apices which are uniformly circumferentially spaced and which extend longitudinally from said other end of said sleeve to said transverse plane,

(d) the wall thickness of said sleeve being reduced at said apices to provide said sleeve with uniformly circumferentially spaced, internal lines of weakness extending longitudinally from said other end of said sleeve to said transverse plane, and

(e) said sleeve being splittable from said other end thereof toward said head along said internal lines of weakness,

(B) a pin extending through said tubular rivet and including (a) grippable means at one end of said pin and protruding from said tubular rivet at the head end thereof,

(b) a breakneck of reduced cross sectional area intermediate the ends of said pin,

(c) a pin head on the other end of said pin and protruding from said other end of said sleeve, for expanding said tubular rivet and for splitting said sleeve from said other end thereof toward said head of said tubular rivet along said internal lines of weakness into separate petals and bending said petals radially outward, in response to axial movement of said pin relative to said tubular rivet in a direction to draw said pin head into said tubular rivet through said other end of said sleeve, and

(d) said pin head being of circular cross section substantially equal in diameter to said sleeve and the portion adjoining said pin being generally frusto-conical converging toward and into said sleeve bore whereby said frustoconi cal portion engages said flat walls along medial lines of Contact during said axial movement of said pin.

2. In a blind rivet assembly, the combination of:

(A) a tubular rivet capable of permanent deformation and including (a) an externally cylindrical sleeve provided with a through bore and having at one end thereof a head with a transverse annular shoulder which faces the other end of said sleeve,

(b) the bore of said sleeve, between said other end thereof and a transverse plane adjacent said head, being substantially square and being dened by four substantially flat walls of substantially equal widths extending from said other end of said sleeve to said transverse plane,

(c) said walls intersecting at apices which are uniformly circumferentially spaced and which extend longitudinally from said other end of said sleeve to said transverse plane,

(d) the wall thickness of said sleeve being reduced at said apices to provide said sleeve with uniformly circumferentially spaced, internal lines of weakness extending longitudinally from said other end of said sleeve to said transverse plane,

(e) said sleeve being splittable from said other end thereof toward said head along said internal lines of weakness, and

(f) said tubular rivet having a circular internal cross section within said head; and

(B) a pin extending through said tubular rivet and including (a) grippable means at one end of said pin and protruding from said tubular rivet at the head end thereof,

(b) a breakneck of reduced cross sectional area intermediate ends of said pin,

(c) a pin head on the other end of said pin and protruding from said other end of said sleeve, for expanding said tubular rivet and for splitting said sleeve from said other end thereof toward said head of said tubular rivet along said internal lines of weakness into separate petals and bending said petals radially outward, in response to axial movement of said pin relative to said tubular rivet in a direction to draw said pin head into said tubular rivet through said other end of said sleeve, and

(d) said pin head being of circular cross section substantially equal in diameter to said sleeve and the portion adjoining said pin being generally frusto-conical converging toward and into said sleeve bore whereby said frusto-conical portion engages said flat walls along medial lines of contact during said axial movement of said pin.

3. In a blind rivet assembly, the combination of:

(A) a tubular rivet capable of permanent deformation and including (a) an externally cylindrical sleeve provided with a through bore and having at one end thereof a head with a transverse annular shoulder which faces the other end of said sleeve,

(b) the bore of said sleeve, between said other end thereof and a transverse plane adjacent said head, being substantially square and being defined by four substantially flat walls of substantially equal widths extending from said other end of said sleeve to said transverse plane,

(c) said walls intersecting at apices which are uniformly circumferentially spaced and which extend longitudinally from `said other end of said sleeve to said transverse plane,

(d) the wall thickness of said sleeve being reduced at said apices to provide said sleeve with uniformly circumferentially spaced, internal lines of weakness extending longitudinally from 1 1 said other end of said sleeve to said transverse plane,

(e) said sleeve being splittable from said other end thereof toward said head along said internal lines of Weakness, and

(f) said tu-bular rivet having a circular internal cross section within said head; and

(B) a pin extending through said tubular rivet and including (a) grippable means at one end of said pin and protruding from said tubular rivet at the head end thereof,

(b) a breakneck of reduced cross sectional area intermediate the ends of said pin,

(c) a pin head on the other end of said pin and protruding from said other end of said sleeve, for expanding said tubular rivet and for splitting said sleeve from said other end thereof toward said head of said tubular rivet along said internal lines of Weakness into separate petals and bending said petals radially outward, in response to axial movement of said pin relative to said tubular rivet in `a direction to draw said pin head into said tubular rivet through said other end of said sleeve,

(d) said pin head being of circular cross section substantially equal in diameter to said sleeve and the portion adjoining said pin being gen- 1 2 erally frusto-conical converging toward and into said sleeve bore whereby said frusto-conical portion engages said flat Walls along medial lines of contact during said axial movement of said pin,

(e) said frusto-conical portion including adjacent said shank a -rst frusto-conical annular surface having an acute included angle, and

(f) said frustoconical portion including adjacent said iirst frusto-conical annular surface a second frusto-conical annular surface having an obtuse included angle.

References Cited in the file of this patent UNITED STATES PATENTS 420,829 Platt Feb. 4, 1890 1,019,723 Pauli Mar. 5, 1912 2,426,422 Huck Aug. 27, 1947 2,586,336 Torrenson Feb. 19, 1952 2,592,130 Erb et al. Apr. 8, 1952 2,635,501 Eichner Apr. 21, 1953 2,652,741 Ketchum Sept. 22, 1953 2,963,935 Shields Dec. 13, 1960 FOREiGN PATENTS 209,951 Australia Aug. 21, 1957 

